Figure 11: Optical micrograph of service exposed CCU reactor (a) base material in as received condition showing ferritic pearlitic structure. (b) base material in crept condition at 78 MPa/ 515°C showing very fine grain structure. (c) base material crept at 98 MPa/ 515°C showing graphite nodule associated with micro-cracks. (d) weld material in as received condition showing microcracks and voids. (e) weld materials crept at 78 MPa/ 515°C showing coarse grains and graphite nodules in the base region and (f) showing transition zone of fine grains in weld region and coarse ferrite (white) grains in base metal regions [15].